The assembly formed by the impulse pin and the pallet fork permits the unlocking of a tooth of the wheel of the escapement mechanism from the lever and the impulse of the balance wheel. During the impulse, the impulse pin, which is connected to the balance, and the pallet fork transmit the energy from the pallet lever to the balance with each vibration.
A conventional system is formed of a circular or “half-moon” pin with a portion of the circle removed to allow the pin to enter inside the fork in a sufficiently secure manner. The fork takes the form of a rectangular notch. The surfaces of contact with the impulse pin are generally flat.
Typically, the contact surfaces between the fork and the impulse pin are identical for unlocking and for the impulse, that is to say that the pair of surfaces in contact when unlocking occurs in the first vibration is identical to the pair of surfaces in contact when the impulse occurs in the second vibration. However, a geometry which might be optimal for the unlocking function, might not be optimal for the impulse function. In conventional systems, the geometry of the impulse pin and the fork is therefore not optimised. The aim of optimising the geometry of the contact surfaces between the impulse pin and the fork, in particular, is to reduce friction in order to reduce the wear of parts, or to reduce energy losses to increase the efficiency of the escapement.
It is an object of the invention to provide a watch escapement mechanism which is accurate and reliable over a long period of use.
It is advantageous to provide a watch escapement mechanism with very low wear.
It is advantageous to provide a watch escapement mechanism with very low power consumption.
It is advantageous to provide a compact and robust escapement mechanism.